Automatic transmission for a vehicle

ABSTRACT

An automatic transmission for a front-engine front-drive vehicle including a fluid coupling, a belt type continuously-variable speed transmission (CVT), a planetary gear mechanism, a forward-reverse changeover mechanism and a differential device. The forward-reverse changeover mechanism includes a brake disposed between the planetary gear mechanism and the output of CVT. The planetary gear mechanism is provided with a low-high speed changeover mechanism. Each of the clutch and the brake is provided with recesses in one part thereof and are provided with projections in the other part which can be fitted into the recesses, and the dimension of the outer diameter thereof is small as compared with that of clutches or brakes of the wet multiple-disc type.

BACKGROUND OF THE INVENTION

The present invention relates to an automatic transmission for a vehiclewhich uses a belt type continuously-variable speed transmission system(hereinafter referred to as "CVT").

The CVT includes an input pulley, an output pulley and an endless beltextended between the pulleys. The input pulley and the output pulleyeach includes a fixed sheave secured to a rotational shaft and a movablesheave mounted movably in an axial direction of the rotational shaft bymeans of a servo motor, and the movable sheave can be displaced axiallyto thereby change the ratio of rotational speed of the output pulleyrelative to that of the input pulley in the range of approximately 0.5to 2.0.

When the CVT is used as the transmission for a vehicle, a firstrotational shaft having the input pulley of the CVT mounted thereon isconnected to an output shaft of an engine through a coupling means, andbetween a second rotational shaft having the output pulley of the CVTmounted thereon and a differential device are provided with a planetarygear mechanism, a forward-reverse changeover mechanism. A low-high speedchangeover mechanism is provided in the planetary gear mechanism, ifnecessary. Generally speaking, the forward-reverse changeover mechanismand the low-high speed changeover mechanism are necessary to providewith a clutch for connecting specific elements of the planetary gearmechanism or a brake adapted to connect a specific element of theplanetary gear mechanism in a stationary position. However, when a wetmultiple-disc type clutch or brake is employed as the aforementionedclutch or brake, it is difficult to load the transmission on a smallautomobile because the diameter of a frictional engaging element of saidwet multiple-disc type clutch or brake is large, resulting in a largedimension of the whole transmission for a vehicle.

What is needed is an automatic transmission for a vehicle wherein aforward-reverse changeover gear mechanism or a low-high speed changeovergear mechanism, which is provided between the rotational shaft havingthe output pulley of the CVT mounted thereon and a transmission outputshaft for a vehicle, is miniaturized and light-weighted.

SUMMARY OF THE INVENTION

Generally speaking, in accordance with the present invention, anautomatic transmission for a vehicle especially suitable for a smallsize, front-engine front-drive automobile provided with a belt typecontinuously-variable speed transmission system (CVT) and a planetarygear mechanism, is provided. The CVT includes an input pulley mounted ona first shaft, an output pulley mounted on a second shaft and an endlessbelt extended between the input pulley and output pulley to transmitpower. The first shaft is disposed coaxially with and coupled to anoutput shaft of a coupling means, and the second shaft is disposedparallel with the first shaft. The input pulley and output pulley eachincludes a fixed sheave and a movable sheave which is well known.

The planetary gear mechanism has its input shaft and output shaftdisposed coaxially with the second shaft of the CVT and includes atleast one forward speed range and one reverse range.

The planetary gear mechanism according to the present invention is ofthe type in which a first element thereof is braked and held in astationary position by means of brake means thereby establishing theforward range whereas a second element is braked and held in astationary position by means of brake means thereby establishing thereverse range. To this end, one end of a first intermediate shaft isconnected to the first element whereas one end of a second intermediateshaft is connected to the second element, the first and secondintermediate shafts being selectively held by the forward-reversechangeover mechanism. The brake means includes a sleeve which isdisposed coaxially with and slidably movable but non-rotatable withrespect to the rotational axis of the input shaft of the planetary gearmechanism and having splines adapted to selectively mesh with splinesformed on the first and second intermediate shafts, whereby the outerdiameter of the brake means is reduced as compared with a wetmultiple-disc type brake means and the braking effect of the brake meansis not impaired.

According to the present invention, a low-high speed changeovermechanism is further provided in the planetary gear mechanism. Thislow-high speed changeover mechanism includes a first and a second discsdisposed perpendicularly and rotatably with respect to a rotational axisof an output shaft of the planetary gear mechanism, a sleeve which ismovable axially of the rotational axis and rotatable integrally with athird element of the planetary gear mechanism and a shift lever havingone end placed in engagement with the sleeve, the first and second discsbeing formed with splines, and the sleeve being formed with splinesselectively engageable with the splines formed on the first and seconddiscs. When the sleeve is shifted by the shift lever to a position wherethe sleeve is selectively connected to the first disc, the first elementof the planetary gear mechanism is connected to the third element toform the forward range gear train whereas when the sleeve is shifted bythe shift lever to a position where the sleeve is selectively connectedto the second disc, the third element of the planetary gear mechanism isconnected to a fourth element of the planetary gear mechanism to formanother forward range gear train.

Accordingly, it is a primary object of the present invention to providean improved and compact automatic transmission having a CVT and aplanetary gear mechanism which automatic transmission is capable ofestablishing a forward range gear train when a first element of theplanetary gear mechenism is selectively held in a stationary position bymeans of brake means and of establishing a reverse range gear train whena second element of the planetary gear mechanism is selectively held ina stationary position by means of brake means.

Another object of the present invention is to provide an improved andcompact automatic transmission having a CVT and a planetary gearmechanism in which the planetary gear mechanism includes the firstelement, the second element, a first intermediate shaft connected to thefirst element, a second intermediate shaft connected to the secondelement and the brake means including splines formed on the first andsecond intermediate shafts, respectively, and a sleeve having splinesadapted to selectively mesh with the splines formed on the firstintermediate shaft to hold the first element in the stationary positionand to selectively mesh with the splines formed on the secondintermediate shaft to hold the second element in the stationaryposition, whereby the outer diameter of the brake means is reduced incompared with that of a wet multiple-disc type brake means.

A further object of the present invention is to provide an improved andcompact automatic transmission having a CVT and a planetary gearmechanism in which the planetary gear mechanism includes the firstelement, the second element, the third element, a fourth element, brakemeans selectively holds the first element and the second element in thestationary position, respectively, and clutch means disposed between thethird element and the fourth element and adapted to establish anotherforward range gear train when the third element is connected to thefourth element by means of the clutch means.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements and arrangement of parts which will beexemplified in the constructions hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a schematic sectional view of an automatic transmission inaccordance with an embodiment of the present invention, and

FIG. 2 is a schematic sectional view of an automatic transmission inaccordance with another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment in which the present invention is applied toan automatic transmission for a vehicle of the front-engine front-drivesystem. This automatic transmission comprises a coupling means 15, abelt type continuously-variable speed transmission system (CVT) 3, aplanetary gear mechanism 8, a differential device 2 and a transmissionhousing 70 for accommodating these elements and fixedly mounted on anengine 1. The housing 70 is partially shown in FIG. 1.

The coupling means 15 is shown in form of a fluid coupling including aninput shaft 16 connected coaxially with an output shaft (not shown) ofthe engine 1 and an output shaft 17 disposed coaxially with the inputshaft 16. Other automatic clutch means such as a torque converter, acentrifugal clutch, a magnetic clutch, etc. can be used in place of thefluid coupling 15.

The CVT 3 comprises an input pulley 31 mounted on a first shaft 4, anoutput pulley 32 mounted on a second shaft 5, and an endless belt 33extended between the pulleys 31 and 32 to transmit power. The pulleys31, 32 each has fixed sheaves 31A, 32A secured to the shafts 4, 5, andmovable sheaves 31B, 32B mounted slidably axially on the shafts 4, 5,respectively. Each of the movable sheaves 31B, 32B is operated byhydraulic servomotor mounted on the shafts 4, 5, respectively. The firstshaft 4 is disposed coaxially with the output shaft 17 of the couplingmeans 15 and coupled thereto. The second shaft 5 is formed in the formof a tubular shaft, which rotational axis is arranged parallel with therotational axis of the first shaft 4.

The planetary gear mechanism 8 has an input shaft 51 and an output shaft52 disposed coaxially with the rotational axis of the second shaft 5 ofthe CVT 3 and has two sets of planetary gear set. The first planetarygear set comprises a first sun gear 81 fixed concentrically with theinput shaft 51, a first ring gear 82 arranged concentrically with thesun gear 81, at least one first planetary gear 83 meshing with the sungear 81 and ring gear 82 and a first planetary carrier 84 for rotatablysupporting the planetary gear 83 thereon. The second planetary gear setcomprises a second sun gear 85 arranged concentrically with therotational axis of the output shaft 52, a second ring gear 86 arrangedconcentrically with the sun gear 85, at least one second planetary gear87 meshing with the sun gear 85 and ring gear 86 and a second planetarycarrier 88 for roratably supporting the planetary gear 87 thereon. Thefirst ring gear 82 and second sun gear 85 are connected to one end of afirst intermediate shaft 53 disposed concentrically with the rotationalaxis of the input shaft 51 and are rotated integrally therewith, and thefirst planetary carrier 84 and second ring gear 86 are connected to oneend of a second intermediate shaft 54 disposed concentrically with therotational axis of the input shaft 51 and are rotated integrallytherewith. The second planetary carrier 88 is connected to one end ofthe output shaft 52. In the planetary gear mechanism 8, when the firstintermediate shaft 53 is braked and held in a stationary position andthe second intermediate shaft 54 is rotated freely, a forward range geartrain is formed for transmitting rotation in the same direction as thatof the input shaft 51 to the output shaft 52, whereas when the secondintermediate shaft 54 is braked and held in a stationary position andthe first intermediate shaft 53 is rotated freely, a reverse range geartrain is formed for transmitting rotation in the direction opposite tothat of the input shaft 51 to the output shaft 52.

The output shaft 52 is formed in the form of a tubular shaft, the otherend thereof is connected to a gear casing 21 of a differential device 2concentrically with the rotational axis thereof. This differentialdevice 2 comprises differential gears 22, 23 secured to a shaftsupported on the casing 21 perpendicularly to the rotational axis of thecasing 21 and output gears 24, 25 rotatably supported on the casing 21with respect to the rotational axis of the casing 21, and meshed withsaid output gears 24, 25, respectively. Output shafts 28, 29 areconnected to said output gears 24, 25, respectively, for connection withan axle (not shown) used to drive front wheels.

The transmission housing, which is not totally shown in FIG. 1 butpartly indicated at 70, is secured to the engine 1. The fluid coupling15 and input pulley 31 of the CVT 3 are rotatably supported on thehousing 70 by means of the first shaft 4 and the output pulley 32 of theCVT 3, planetary gear mechanism 8 and differential device 2 arerotatably supported on the housing 70 by means of the second shaft 5 andoutput shaft 52.

A forward-reverse changeover mechanism 7 is formed between the outputpulley 32 of the CVT 3 and the planetary gear mechanism 8. The mechanism7 includes splines 74, 75 which are formed on the outer circumference ofthe other end of the first intermediate shaft 53 and on the outercircumference of the other end of the second intermediate shaft 54,respectively, a sleeve 72 which is disposed concentrically with andmovable axially of the rotational axis of the input shaft 51 of theplanetary gear mechanism 8, splines 73 formed on the inner circumferenceof the sleeve 72 and selectively engageable with the splines 74, 75, anda shift lever 71 one end of which is engaged with the sleeve 72 througha shift ring 79. The sleeve 72 has a key 76 formed axially andintegrally therewith, said key is fitted into a groove 77 formed in thehousing 70, and cannot be rotated with respect to the rotational axis ofthe input shaft 51. When the shift lever 71 is operated to move thesleeve 72 in a direction as indicated by the arrow D shown in FIG. 1 inthe direction of the rotational axis, he splines 73 formed on the innercircumference of the sleeve 72 comes to mesh with the spline 74 formedon the outer circumference of the first intermediate shaft 53 to holdthe first intermediate shaft 53 in the stationary position so that thesecond intermediate shaft 54 can be rotated freely, and hence theforward range gear train is formed. When the sleeve 72 is moved in adirection of arrow R which is opposite the arrow D, the splines 73formed on the inner circumference of the sleeve 72 comes to mesh withthe splines 75 formed on the outer circumference of the secondintermediate shaft 54 to hold the second intermediate shaft at thestationary position so that the first intermediate shaft can be rotatedfreely, and hence the reverse range gear train is formed. The other endof the shift lever 71 projects beside the driver's seat of the vehicle.

The embodiment of the present invention shown in FIG. 1 operates asfollows. The engine 1 of the vehicle is started and the lever 71projecting besides the driver's seat is positioned to the forward orreverse position to move the shift ring by a driver. If the engine 1 isin the idling mode, engine torque generated by the engine 1 may not betransmitted to the input pulley 31 of the CVT 3 through the fluidcoupling 15, and therefore, the sleeve 72 of the forward-reversechangeover mechanism 7 is readily spline-coupled with the firstintermediate shaft 53 of or second intermediate shaft 54 of theplanetary gear mechanism 8 to hold the first intermediate shaft 53 orsecond intermediate shaft 54 in the stationary position. Next, anaccelerator pedal is pressed down by the driver, the engine torque istransmitted to the input shaft 4 of the CVT 3 by means of the fluidcoupling 15 when the throttle opening of the engine 1 exceeds apredetermined value, and the vehicle starts to move. As is known, theCVT 3 continuously varies the ratio of rotational speed between theinput shaft 4 and output shaft 5. The engine torque transmitted to theoutput shaft 5 of the CVT 3 is transmitted to the front wheels throughthe planetary gear mechanism 8, differential device 2 and output shafts28, 29.

In the above-described transmission, the changing-over of the forwardrange drive and reverse range drive of the planetary gear mechanism 8 isachieved in such a way that the splines 73 formed on the sleeve 72 ofthe forward-reverse changeover mechanism 7 is selectively meshed withthe splines 74 formed on the first intermediate shaft 53 or the splines75 formed on the second intermediate shaft 54 to selectively hold theintermediate shafts 53, 54 in the stationary position, and therefore,the dimension of the outer circumference of the forward-reversechangeover mechanism 7 can be considerably reduced and the force forbraking the first intermediate shaft 53 or second intermediate shaft 54can be considerably increased.

FIG. 2 shows another embodiment of the present invention in which alow-high speed changeover mechanism 9 is further provided in theplanetary gear mechanism 8 shown in FIG. 1. Accordingly, detailedexplanations for parts common to those of the embodiment shown in FIG. 1will be omitted.

The low-high speed changeover mechanism 9 includes a first and a seconddiscs 93, 94 formed on the inner circumferences thereof with splines 96,97, respectively, a second sleeve 92 disposed concentrically withrespect to the rotational axis of the output shaft 52 of the planetarygear mechanism 8 and formed on the outer circumference thereof withsplines 98, 99 for selectively meshing with the splines 96, 97 formed onthe two discs 93, 94, respectively, and at least one guide pin 95loosely supported on the sleeve 92. The first disc 93 is connected tothe first ring gear 82 of the planetary gear mechanism 8, the seconddisc 94 is connected to the second planetary gear 88, and each of thefirst and second discs 93, 94 is rotatable concentrically with respectto the rotational axis of the output shaft 52 and has a mean planethereof in a plane vertical to the rotational axis of the output shaft52 of the planetary gear mechanism 8. The second sleeve 92 isspline-coupled axially slidably to the second sun gear 85 of theplanetary gear mechanism 8 and is rotatable integrally with the sun gear85. A shift ring 91 is relatively rotatably engaged with a groove formedon the outer circumference of the second sleeve 92 and is operated bymeans of a shift lever 100 directly or indirectly associated with theshift lever 71 to shift the sleeve 92 in a direction of L or H, which isindicated by the arrow in FIG. 2. When the sleeve 92 is shifted in thedirection of the arrow L, the splines 98 formed on the sleeve 92 comesto mesh with the splines 96 formed on the first disc 93 to connect thefirst ring gear 82 with the second sun gear 85 whereby the second disc94 may be rotated freely thereby the same forward range gear train asthat of the planetary gear mechanism 8 shown in FIG. 1 is formed. Whenthe sleeve 92 is shifted in the direction of arrow H, the splines 98formed on the sleeve 92 is moved away from the splines 96 formed on thefirst disc 93 to rotate the first disc 93 and the first ring gear 82freely and the splines 99 formed on the sleeve 92 comes to mesh with thesplines 97 formed on the second disc 94 to connect the second carrier 88to the second sun gear 85 of the planetary gear mechanism 8 thereby thesecond planetary gear set is interlocked, and hence a forward rangehigh-speed gear train is formed. The guide pin 95 is disposed betweenopposed surfaces of the first and second discs 93, 94 with thelengthwise direction thereof being parallel with the rotational axis ofthe output shaft 52. When the sleeve 92 is shifted in the direction ofarrow L or H, one end of the guide pin 95 comes to abut with either thefirst disc 93 or the second disc 94 whereby the rotational speed of thedisc is synchronized with the rotational speed of the sleeve 92 tofacilitate the spline-coupling between the sleeve 92 and the first disc93 or the second disc 94. That is, the low-high speed changeovermechanism 9 corresponds to a dog clutch having the function of asynchronizer.

In the embodiment shown in FIG. 2, the upshift from the forward rangelow-speed gear train to the forward range high-speed gear train or thedownshift from the forward range high-speed gear train to the forwardrange low-speed gear train is carried out by moving the second sleeve 92in its axial direction through the shift lever 100 or shift ring 91. Inthis operation, one end of the guide pin 95 loosely supported on thesecond sleeve 92 comes into contact with one surface of the first disc93 or second disc 94 to thereby synchronize the rotational speed of thedisc in contact with the guide pin 95 with the rotational speed of thesecond sleeve, and thereafter, the splines formed on the second sleeve92 is brought into engagement with the splines 96 formed on the firstdisc 93 or the splines 99 formed on the second sleeve 92 into engagementwith the splines 97 formed on the second disc 94. Therefore, theengagement between these splines is extremely easily and positivelyeffected.

What is claimed is:
 1. An automatic transmission for a vehicle,comprising:a coupling means having an input shaft and an output shaft; abelt type continuously-variable speed transmission system having aninput pulley mounted coaxially on a first shaft, an output pulleymounted coaxially on a second shaft and a belt extending between saidfirst and second pulleys to transfer power, each of said first andsecond pulleys having a fixed sheave and a movable sheave, said firstshaft being disposed coaxially with and rotatably coupled with saidoutput shaft of said coupling means, said second shaft being disposedside by side and in parallel with said first shaft; a planetary gearmechanism having a first planetary gear set including a first sun gear,a first planetary gear, a first ring gear and a first planetary carrier,a second planetary gear set including a second sun gear, a secondplanetary gear, a second ring gear and a second planetary carrier, aninput shaft disposed coaxially with and rotatably coupled at one endthereof with said second shaft of said belt type continuously-variablespeed transmission system connected at the other end thereofconcentrically with said first sun gear, an output shaft disposedcoaxially with said input shaft and connected at one end thereofconcentrically with said second planetary carrier, a first intermediateshaft disposed concentrically with and radially outward in connectionwith said input shaft and connected at one end thereof with said firstring gear and said second sun gear and a second intermediate shaftdisposed concentrically with and between said input shaft and said firstintermediate shaft in radial direction and connected at one end thereofwith said first planetary carrier and said second ring gear, each ofsaid first and second intermediate shaft having splines on an outercircumference thereof at the other end which is positioned between saidoutput pulley of said belt type continuously-variable speed transmissionsystem and said planetary gear mechanism; a forward-reverse changeovermechanism having one and single shift lever and one and single firstsleeve, said first sleeve being positioned between said output pulley ofsaid belt type continuously-variable speed transmission system and saidplanetary gear mechanism and disposed concentrically with and slidablymovable but nonrotatable with respect to the rotational axis of saidinput shaft of said planetary gear mechanism and having splines on aninner circumference thereof adapted to selectively mesh with saidsplines formed on said first and second intermediate shafts, said shiftlever being adapted to shift said first sleeve between a first positionwhere said splines formed on said first sleeve is selectively meshedwith said splines formed on said first intermediate shaft to hold saidfirst ring gear and second sun gear in a stationary position toestablish a forward range gear train and a second position where saidsplines formed on said first sleeve is selectively meshed with saidsplines formed on said second intermediate shaft to hold said firstplanetary carrier and said second ring gear in a stationary position toestablish a reverse range gear train, and a low-high speed changeovermechanism having a second sleeve disposed concentrically with andslidably and rotatably with respect to the rotational axis of saidoutput shaft of said planetary gear mechanism, a first and second discsdisposed perpendicularly to and rotatably with respect to the rotationalaxis of said output shaft of said planetary gear mechanism,respectively, and a shift lever being engaged with said second sleeve atone end thereof, said first disc being linked to said first ring gearand having splines on an inner circumference thereof, said second discbeing linked to said second planetary carrier and having splines on aninner circumference thereof, said second sleeve being slidably connectedto and integrally rotatable with said second sun gear and having splineson an outer circumference thereof and adapted to selectively mesh withsaid splines formed on said first and second discs, said shift leverbeing adapted to shift said second sleeve between a first position wheresaid splines formed on said second sleeve is meshed with said splinesformed on said first disc to establish a forward speed range gear trainand a second position where said splines formed on said second sleeve ismeshed with said splines formed on said second disc to establish anotherforward speed range gear train.
 2. An automatic transmission as claimedin claim 1, wherein said low-high speed changeover mechanism furtherincludes at least a guide pin disposed between said first and seconddiscs in a direction parallel with the rotational axis of said outputshaft of said planetary gear mechanism and being loosely supported onsaid second sleeve whereby said guide pin contacts selectively with oneof said first and second discs for synchronizing the rotational speed ofsaid disc and said second sleeve when said second sleeve is shifted toone of said two positions.